Pilot-Scale Aluminothermic Production of Silicon Alloy and Alumina-Rich Slag

As global demand for silicon (Si) and alumina continues to surge, the significance of developing more sustainable production methods has intensified. The SisAl process represents a path-breaking approach to producing Si and alumina by utilizing side streams from the silicon and aluminum industries. In the present work, a comprehensive series of pilot-scale trials was conducted to assess the scalability and validity of the SisAl process. The influences of reductant raw materials, charging methods, input material ratios, and other processing parameters were also investigated. On coupling between thermodynamic calculations and experimental results, it was demonstrated that the SisAl process is stable and controllable at a pilot scale. The typical composition of the produced Si alloy ranges from 70 to 75 wt % Si, 15-18 wt % Ca, and 8-10 wt % Al. The produced CaO-Al₂O₃-based slag has a composition of 48-57 wt % Al₂O₃, 40-45 wt % CaO, and 3-13 wt % SiO₂. Furthermore, various reductants, including Al blocks, dross, and scraps, were evaluated in the pilot trials, yielding comparable outcomes, with alloy composition differences only within approximately 3 wt % under the same parameter conditions, demonstrating the versatility of raw materials selection in the SisAl process. Moreover, it was found that acidic slag exhibited better features for future upscaling than the neutral slags, with a 5 wt % higher Si content in the alloy and a 4 wt % increase in Al₂O₃ content in the slag phase. Additionally, the chemical composition of the products was shown to be controllable by adjusting the stoichiometry of the input materials (Al/SiO₂ ratio). As the charged stoichiometry increases from 1 to 1.2, the Si content in the alloy significantly decreases from 73 to 63 wt %, while the Al content correspondingly increases from 9 to 18 wt %. Further investigation into processing parameters, such as charging method, slag prefusion, and stirring methods, has also revealed valuable insights toward the continued upscaling of the SisAl process to a potentially innovative, sustainable, low-carbon industrial process.